Often, a blood processing or apheresis instrument is used to separate blood components from whole blood. Such instruments, also known as “separators”, typically separate a selected blood component(s) from whole blood by passing the blood of a donor through the instrument to separate one or more blood components from the whole blood under the influence of centrifugal force or other means for effecting separation. The remainder of the whole blood is then returned to the circulatory system of the donor. It is, therefore, an extracorporeal blood component collection process. Apheresis instruments are commercially available from various sources, including the Amicus® Separator which is available from Fenwal Inc., of Lake Zurich, Ill.
Instruments such as the Amicus Separator may utilize a single-use apheresis kit for collection of a desired blood component. The instrument may have pumps, clamps, and valves that move and direct donor blood through the kit. Such single-use kits are often referred to as “disposables”. Connected to such a kit may be one or more fluid supply containers of replacement fluids for infusion into the donor. A therapeutic plasma exchange (TPE) procedure may require multiple containers of fluid, typically albumin or fresh frozen plasma, to replace potentially up to three or more liters of the patient's waste plasma.
During an apheresis procedure, one of the most significant concerns is prevention of an air embolism. To reduce the risk of air embolism, it is vital to ensure that air does not enter the apheresis disposable kit during a blood component collection procedure. For example, air can be drawn into the disposable kit during a collection procedure when the fluid source, or fluid supply container attached to the kit becomes exhausted of fluid.
During therapeutic apheresis procedures, a patient's particular blood component of interest, such as plasma, is continuously removed while a replacement fluid, which in the case of plasmapheresis is normal plasma or albumin, is continuously infused. In current practice, two replacement fluid supply containers are usually connected to the disposable kit. Replacement fluid is drawn from one container while the other container is clamped. The operator must closely monitor the fluid level in the “active” container. When this container empties, the operator must close its clamp while opening the clamp on the other container. If the operator is occupied with the patient, or otherwise distracted, and does not perform this operation, a large volume of air may be drawn into the disposable kit, requiring air to be purged.
Apheresis instruments are typically equipped with air detection systems that continually monitor the fluid that is being returned to the donor/patient. If, during a procedure, air reaches the air detection system, blood processing is interrupted until the air is purged from the system. Often multiple air purges are required to clear this air. Since blood is not being processed during these purges, the overall procedural efficiency of the blood collection procedure is decreased.
It is known to provide an apparatus and methods for automatically determining when a fluid container becomes empty and to terminate further use of the empty container. It is further known to provide an apparatus and methods for determining when a fluid container becomes empty independent of the size, volume or composition of matter of the container and to switch to a full container if available. See U.S. Patent Application Publication No. 2009/0212070, which is incorporated herein by reference in its entirety. While such an apparatus and method is an improvement over prior apparatus and methods, stopping and or switching fluid flow may occur even though the fluid container is not empty, but merely has a slow flow rate due to, e.g. the viscosity of the fluid being high, a poor spike connection with the fluid container, or other reasons.
Accordingly, it would be desirable to provide an apparatus and system and/or method that is less likely to terminate further use of a fluid container when the container is not empty and avoid such “false switches.” It would also be desirable to provide a system that alerts the operator of: a low weight on both replacement fluid containers; a low weight in the “second” container (i.e., the container that is to be switched to) which may be an indication that no such “second” container is present; and a low flow from a “current” container that would cause a switch when switching from the previous container occurred in less than a predetermined time.